The three year average daily generation and usage now look like this (click to enlarge)
(recall that "usage" is not a clearly defined quantity).
The best fit sine waves to generation and usage, plotted on the graphs, are (click to enlarge):
Well, the upfront money-in-pocket from the FIT is now well over £5/day. What we save from using free rather than costed power, and pushing surplus into the grid, is as ever secondary and difficult to pinpoint, but is certainly another positive quantity. We're not regretting this purchase.
There seems little point in perpetuating this project as I am now confident of the results. This will leave space on the fridge when I no longer stick the daily recording sheet there. Suggestions?